It's definitely not overheating. I tried two logic boards and each with two separate fans in two separate top cases. All combinations resulted in the same... one top case configuration has the fan spinning fast and the other does not. It doesn't matter which logic board is in which case.

I've been messing with them all day trying to figure it out. I'm starting to think there must be some kind of temp sensor in the top case that is blown in one top case and not in the other...

Thanks. I tried all the hardware (logic board, fans, etc.) in two separate top cases. The same logic boards are both functioning correctly in one top case and both function incorrectly in the other top case.

I thought about overheating as well but I felt the air coming out of the fan and it was not hot at all. So I don't think it's that.

AFAIK Temp sensors are on the logic board (should be moving from case to case), the top case contains no temperature sensors. Could one case be shorting a spot on the logic board? (Burr or long screw in a short hole?)

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